By now, modern still and film cameras have such high-resolution image sensors (for example, so-called “4K” (approximately 3840×2160 pixels) or even “8K” (approximately 7680×4320 pixels) in the case of film cameras and up to 40 megapixels in the case of single-lens reflex cameras) that the image sharpness achieved thereby in conjunction with lenses of the highest image quality may even be bothersome in various application scenarios. Although the full image resolution is desired for specific film genres or specific scenes, for example for nature or landscape recordings, it may have a bothersome effect in other scenes, for example portraits.
In order to reduce a bothersome sharpness, cameras may be provided with devices for obtaining an adjustable soft focus effect, for example using software which electronically blurs a recorded image. However, electronic blurring is not comparable with purely optical blurring as the distance of the object from the lens is also incorporated into the result in the case of the purely optical blurring and hence a type of three-dimensional effect arises.
Purely optical blurring may be achieved using so-called soft focus lenses which typically have adjustable air gaps in the lens. However, such soft focus lenses also have unwanted side effects since field-dependent image aberrations such as coma or astigmatism are generated. Moreover, in this implementation, it is difficult, as a result of variable air gaps, to prevent an occurrence of defocusing in addition to the desired spherical aberration, it only being possible to compensate the defocusing with much outlay by way of data tables and a complicated structure of the system. Hence, on account of the existing coupling between the soft focus effect and the field-dependent image aberrations, lenses with adjustable air gaps do not reach the original maximum image sharpness of the lens, or only do so with significant additional outlay, that is, with additional lens elements.